1. Field of the Invention
The present invention relates to a sensor and a detecting method; and particularly relates to the sensor for a sandwich immunoassay with the use of an enzyme-linked secondary antibody, which is an array-type sensor device for detecting a plurality of objective substances to be detected on the same device, and electrochemically detects a product formed by an enzyme reaction with an electrode, and to the detecting method.
2. Related Background Art
A detecting technique using an enzyme electrode method is known as a method for detecting a substance in a solution. The enzyme electrode method comprises immobilizing an enzyme on an electrode, making an enzyme substrate react with the immobilized enzyme, and measuring the amount of a reaction product by a current flowing through the electrode. The amount of the reaction product is proportional to the amount of the enzyme substrate, so that the amount of the enzyme substrate can be determined from the amount of the reaction product. Accordingly, in the detecting method, the objective substance to be detected is limited to the enzyme substrate.
A method for measuring other objective substances to be detected than an enzyme substrate includes a technology for detecting a plurality of antigens in a solution with electrodes placed on the same substrate, which is an array technology by an enzyme immunoassay, for instance. The array technology comprises immobilizing a kind of antibody on an electrode; reacting the immobilized antibody with a kind of antigen in a sample; reacting a secondary antibody with a captured antigen; and detecting a reaction product formed by the enzyme reaction of the secondary antibody with the electrode, to measure the concentration of the antigen. The array technology using the enzyme immunoassay is shown by Karube et al. in “Analytical Chemistry” 2003, 75, p. 1116–1122.
In order to detect various antigens on the same device by using an array sensor for an electrochemical immunoassay, it is necessary to narrow the space between working electrodes so as to increase the number of antigen species per unit area. On the other hand, an enzyme-reaction product diffuses which has been formed through an enzyme reaction by a secondary antibody coupled to the antigen captured by an immobilized antibody on a certain electrode. However, when the space between the working electrodes is narrow, a so-called crosstalk occurs which is a phenomenon of detecting the diffused enzyme-reaction product on an adjacent electrode.